The present invention relates generally to a method of and apparatus for controlling the application of processing fluid of the type for processing photographic film. More specifically, it is directed to a method of and apparatus for insuring that a preselected length of film is processed by a predetermined quantity of preselected and easily oxidizable processing fluid, while minimizing the detrimental effects of oxidation of such fluid on processing operations.
A variety of photographic processes of the self-developing type broadly involve the application of a viscous liquid reagent across exposed photographic sheet material. Ordinarily in these processes a photosensitive sheet is first exposed and then later superposed with respect to a second sheet. The two superposed sheets are then moved between a pair of juxtaposed pressure applying members. Prior to the sheets moving between the pressure applying members processing fluid is introduced to and between them. The pressure applying members are constructed and arranged to spread the fluid in an approximately uniform layer over a desired exposed portion of one of the sheets. The spread of processing fluid initiates formation of visible images in one of the two sheets.
Significant problems can arise, however, with handling and distributing such a fluid. For example, the fluid is quickly oxidized upon exposure to air. Once oxidized the fluid hardens in the dispensing system and, therefore, subsequent accurate dispensing is impeded. The likelihood for hardening increases somewhat when the film processing operation is intermittent since there is a greater chance of contact with the ambient air.
Attempts have been made to effectively seal the pressurized fluid in the distribution lines particularly with valve systems that permit intermittent dispensing. Representative examples of such approaches are disclosed in the following commonly-assigned U.S. Pat. Nos. 2,435,719; 2,558,858; 2,563,343; 2,719,789; 3,210,792; 3,453,138; 3,142,242, and 3,648,584.
While, in general, such valve systems perform satisfactorily there remains nonetheless a problem in that hardening of even small amounts of fluid can hamper desired sliding movement of valve parts which contact the fluid. Stuck valves obviously hinder desired dispensing, but even worse increase the potential of exposed film portions being unprocessed or undesired flow of processing fluid contacting and contaminating other processing components.
In processing photographic film of the self-developing type, the fluid used should be matched chemically to the sensitivity of the film for optimum processing results. It becomes important, therefore, to have a system that permits each roll of film developed to be processed only by the chemically correct processing fluid. Moreover, it is desired to insure that an entire roll is processed with the correctly matched processing fluid in a manner easily handled by non-technical personnel.